How many PSUs are installed in the Poweredge server? In the manual it says it could be 1 or 2 and the power per PSU could be 1100W so if it is 2 * 1100W then that could explain why the UPS has problems with it.

NetworkManager’s Gnome GUI works with wireguard config files. If you are using Plasma you would need to install some alpha software to do that in the gui but you can always fall back to nmcli which also supports wireguard configs via the import command.